The specific activity of the fatty acid cyclooxygenase catalyzing the initial step in prostaglandin formation is 2-5 fold greater in guinea pig and sheep uteri at the onset of luteolysis than during earlier stages of the estrous cycle. We plan to establish whether this increased activity represents either an increase in the level of cyclooxygenase protein or a decrease in the level of an enzyme inhibitor. To distinguish between these possibilities, we propose to use rabbit anti-cyclooxygenase serum to determine if uterine cyclooxygenases from animals in different stages of the estrous cycle are equivalent immunochemically. We also plan to complete the implementation of a cell culture system which can then be used to determine the rates of cyclooxygenase degradation using common radioimmuno-chemical procedures. A portion of the proposed research will involve our continued use of immunohistochemical techniques to localize sites of prostaglandin formation within tissues particularly those involved with female reproductive function. BIBLIOGRAPHIC REFERENCES: Smith, W.L. and Wilkin, G.P. (1977). Immunochemistry of Prostaglandin Endoperoxide-forming Cyclooxygenases: The Detection of the Cyclooxygenases in Rat, Rabbit and Guinea Pig Kidneys by Immunofluorescence, Prostaglandins, in press. Smith, W.L. and Wilkin, G.P. (1977). Distribution of Prostaglandin-forming Cyclooxygenases in Rat, Rabbit and Guinea Pig Kidney by Immunofluorescence., Fed. Proc., (Abstract), in press.